Some Notes On Australia and Australian Plants
Australian plants currently in production:
Australia is the hottest, flattest, and driest continent. Its soils are almost all old and depleted, and it has been drifting eastward alone for millions of years since separating from its southern hemisphere neighbors.
It is a very diverse and colorful land, with some of the most beautiful plants on the planet. The state of Western Australia is a very special place, with a diversity in many areas equal to that of the tropics and an almost disorientingly brilliant display of wildflowers and flowering shrubs in spring. While their annuals and bulbs are nowhere near as common or diverse as ours, the variety of small flowering woody perennials and small shrubs is almost incomprehensible. There are literally thousands of other plants similar to Boronia megastigma waiting to be discovered by plant lovers in other parts of the world.
Many of these plants are well adapted to California. Australian plants have been selected for dry conditions for much longer than those of California, and the results are easily seen. In central California woodlands Eucalyptus globulus reaches three or four times the height of the native vegetation, easily outcompeting it for light, water, and nutrients.
Of course, many of these plants left the insect pests and grazing herbivores back in Australia, giving them even more of an edge over our native plants. But as we gradually see more and more of these pests follow these Australian natives to our state we will almost certainly see the continued dominance of Australian plants in certain situations. Some Australian plants are simply better at making a living under some of the conditions found in California.
It should be stressed, however, that very few Australian plants have succeeded in naturalizing in our state to more than a very limited degree. Even the notorious Eucalyptus globulus and Acacia mearnsii/decurrens (habit, closeup) have only successfully colonized an extremely small percentage of our land, and are usually restricted to more recently disturbed areas. In almost all areas where they are found, Blue Gums are largely confined to tracts where they were originally planted. The reason? Most Australian plants can't successfully compete in the wild here because of our extended summer drought. Those which have evolved to tolerate the drought come from areas with much less winter rain and will either be overgrown by our native plants or have problems with excess soil moisture. Frost is also a limiting factor in most areas.
Australia is about the size of the continental United States, with a population of around 20 million, roughly two thirds that of just California. About half the continent has a climate which could be called Mediterranean to some degree. Most of the rest would be characterized as either dry tropics, desert, or prairie/steppe. In the western and southwestern regions of Western Australia and the Grampians Mountains of the southeastern corner, where the plant diversity is highest, the climate resembles that of Central and Southern California very closely.
In this catalogue we have made an effort to list the origin of the plants for those who know or are learning about the biogeography of Australia. The northern regions of Australia are similar to our southern states in climate, except that northern Australia is deeply tropical. The southeastern corner (South Australia, Victoria, New South Wales, and part of Queensland) is more continental than much of California, with colder, wetter winters and hotter, more humid summers. Occasional rain is common there during the summer. Overall, however, the climate is still Mediterranean in nature.
The lower half of Western Australia has a climate that is very similar to that of Central or Southern California. Winters are somewhat wetter and warmer. Perth gets an average of about 40 inches of rain a year, and civic landscapes commonly include cultivars of Chamelaucium uncinatum, plants which would not survive in many areas in California without winter protection.
In all areas, the farther away from the coast one gets the hotter the summers become and the colder the winters will be. Plants from the Nullarbor Plains or neighboring regions on the southern edge of the continent will tolerate extreme conditions.
Tasmania, off the extreme southeastern tip of the continent, has a more maritime climate. Many plants from that island can take heavy freezes and even continuous rain. Most can tolerate some summer drought, though, and will adapt quite well to California gardens.
Australian soils are usually quite lean. Plants have adapted to be extremely conservative of some elements (especially phosphorus) and be insensitive to others (especially iron). These nutrient preferences are probably the second most important reason why Australian plants fail to thrive in American gardens, the most common reason being susceptability to root rots, primarily Phytophthora.
In general, almost all Australian plants can tolerate light to moderate doses of fertilizers as long as they are low in phosphates. Most California soils are rich in phosphate by Australian standards, and supplemental applications will usually hinder growth. Such applications can even be enough to damage or kill plants.
Phosphate toxicity is indicated first by interveinal yellowing of the foliage, followed by blackening of the leaves and twigs. Death will result eventually. If a plant is suspected of being poisoned by phosphate, immediate applications of almost any form of iron will usually cure the problem. Iron and phosphate form a molecular complex, and render each other unavailable, both in the soil and in the leaf.
We recommend a soluble iron/trace element chelate spray treatment for short term treatment of yellow plants. Use a light rate and wait a couple of weeks between applications. Plants can be killed or burned by strong iron solutions! Plants usually respond favorably by producing new, dark green growth. Iron is usually present in the soil but complexed with another element and unavailable to the plants, especially at higher pH. Applications of sulfur will usually cure the problem in the long run by making the soil more acid. Unfortunately, the form of iron sold in retail, which uses the chelating agent EDTA, is particularly ineffective. The best stuff uses EDDHA as a chelating agent.
Magnesium deficiency can also be present in Australian natives in many California soils. Epsom salts can be used to cure this problem.
A result of adaptation to low nutrient levels is that some of the smaller Australian woody shrubs and perennials will need help with weed suppression in our richer soils, through the use of either mulch or preemergents. If the plants are grown in soils with low nutrient levels, and fertilizing is kept to a minimum, weeds should be much less of a problem.
Some of our plants are noted to have come from the sand hills of Western Australia. These areas have very open soils, often consisting of pure white sand, with sharp drainage and low nutrient levels. Some plants found in these sands can be tricky to grow with less than perfect drainage. Other times, these plants are found in the sand hills only because they cannot compete with other plants in richer, moister soils. They often can grow just fine in heavier soils in cultivation.
Sandy soils can also overlay laterite. Laterite gravels are composed of iron rich materials, often in the form of small, round nodules, which erode into either light tan or dark red earth. Slopes covered with these ball bearing-like nodules are often quite slippery to walk on. These soils are thought to form as the result of eons of leaching of all soluble nutrients by rainfall under hot, tropical conditions. In these gravels, drainage can often be slow. Plants native to these soils stand a good chance of surviving in poorly drained soils. (Another result of this leaching and iron enrichment is very low levels of available nitrogen and phosphorus.)
Most of the Australian plants we grow will take frost to at least 25°F, which means that they will start showing moderate to severe damage at that temperature. These plants should be good choices for use in coastal areas of Northern California as well as most of Southern California. The showiest of these plants, those worthy of a site with overhead protection, would also be successful in colder areas such as the Sacramento and San Joaquin Valleys. Only a couple of our plants need almost total frost protection, and we only carry those because they are so nice they are well worth the effort.
The rest of the group will generally tolerate 20°F with varying degrees of damage. This will extend the areas where they can be considered permanent members of the landscape to the Delta, all of the San Francisco Bay Area, most of the Central Valley, and the inland areas of Southern California.
A few plants from Australia will tolerate 15°F without serious damage, mostly those plants from high altitude on the southeastern side of Australia or especially those from the island of Tasmania, off the southeastern tip. One Australian plant maniac languishing in the Washington D. C. area informs us that Grevillea australis and G. victoriae, both of which have high altitude populations in southeastern Australia as well as Tasmania, took 6°F in a storm there without appreciable damage. In general, however, 15-20°F seems to be the lowest one can reasonably expect from the continental flora.
Readers will notice that the vast majority of our Australian plants were introduced through the Arboretum at UC Santa Cruz. We strongly encourage nurseries and plant collectors to support their efforts through donations or purchases at their plant sales.
Some other Australian plant links:
Some of the best books on Australian plants are:
Plant Life of Western Australia, by J.S. Beard. This 320 page book by a former director of Kings's Park Botanic Garden in Perth is just crammed with great pictures and examples of typical Western Australian plant/soil associations as well as individual closeups of spectacular individual species and specimens. If you had to go to Western Australia with just one book, this would be the one. Its discussion of soil types, their development, and their associated plants is just superb. It covers the full range of Western Australian habitats, from seaside to desert, tropical swamp land to southern coast. I wish I had had this book when I was there! This is easily the best book of the lot, and one of the best ever published, for showing what Australian plants look like in the wild. Leafing through its pages sends me back to when I was wandering slowly through the spectacular blooming plantscapes of Western Australia, with its clear, clear air, puffy broken clouds whisking quickly against a deep blue sky, and light winds softly whistling through the leaves and branches. Every step brought a new species or even genus, usually in full bloom, or with wonderful new growth or seed pods, or extraordinary form. If you can't go to see for yourself, this book is the next best thing.
The Australian Gardener's Wildflower Catalogue by Denise Greig. This luscious, 343 page full color treatment of the species selections and hybrids commonly found in the trade in Australia is the best I have found yet at conveying the unrelenting beauty of Australian plants. The author is a professional photographer (it shows) and author on native flora. The plants are arranged in alphabetical order, with almost all of the varieties described represented by individual pictures. The layout is clean and visually pleasing. Many of the plants shown are sold in the United States, although many others are either unknown, are very rarely raised here or haven't lasted in the trade. Many of the varieties not currently available commercially can be seen in botanic gardens throughout California. As far as I know, this book is still unavailable in the US, so you will have to pick it up over there. It is available as hard or soft cover. Its only deficiency is that the parameters for cultivation use relative terms, so you have to know something about Australian climatic zones to understand what such phrases as "frost-resistant" and "warm coastal" mean.
The Grevillea Book, by Peter Olde & Neil Marriott. Peter Olde is the leader of the SGAP's (Society for Growing Australian Plants) Grevillea Study Group, Neil Marriott is a Victorian nurseryman and former owner of the renowned White Gums Nursery. This is a definitive work on Grevilleas, with three volumes. Volume One discusses history, evolution, biology, and general cultivation. The second and third volumes are an alphabetical treatment of all the species, from description to distribution and cultivation. It is by definition a good book because the authors included the defining feature of a good botanical descriptive work: how each species differs from others, especially those closely related or easily confused. Words cannot express how grateful I am to find they had the sense to include this most important feature usually found missing in books otherwise excellent. The deficiency of these books is that they doesn't consider hybrids, although I have heard rumors that such a work is in progress. Until that shortcoming is covered, there is a major need not being filled, although most are covered by the following work:
Encyclopaedia of Australian Plants suitable for cultivation, by Rodger Elliot and David Jones. In six (now seven?) volumes through the letter M, each volume around 500 pages. Easily the most exhaustive and complete source of information on Australian plants actually in cultivation, soon to be in cultivation, or with even a prayer of a chance of being introduced to cultivation. Contains great line drawings by the indomitable and inimitable Trevor Blake, great pictures by Rodger and David, and very accurate biogeographical cultivation information or hints as to successful culture or propagation. Rodger Elliot is a former owner of Austraflora Nursery, another renowned Australian native wholesale/retail nursery, and a noted author on native flora. Rodger is involved with Koala Blooms, a business which creates and popularizes Australian native plant hybrids and selections for use in the greenhouse and nursery trades around the world. David Jones is another excellent nurseryman with a wide reputation who has special interests in ferns, orchids, and flora of the tropical regions.